Macro-modelling of combined in-plane and out-of-plane seismic response of thin strengthened masonry infills

Some strengthening techniques, aimed to increase the infill Out-Of-Plane (OOP) resistance and its safety against OOP collapse, have been recently tested at the University of Padova. Based on this experimental work, a new infill macro-model consisting of two nonlinear fibre struts for each diagonal direction, able to predict the combined In-Plane/Out-Of-Plane (IP-OOP) seismic response of the panels, is proposed in this paper and calibrated on the above-mentioned experimental results for thin clay masonry panels strengthened by two external plaster layers, directly applied on the masonry surface, containing a biaxial basalt fibre grid. These macro-models were then used to carry-out parametric nonlinear static analyses on typical reinforced concrete infilled frames, designed both traditionally and seismically, with the aim of evaluating their lateral response both in the case of IP forces only (by assuming two force distributions applied to the frame) and in the case of IP-OOP combined forces (by applying OOP equivalent static forces to the panels). The main effects of the OOP forces are presented through pushover curves and drift profiles associated to the achievement of the various infill and frame limit states. Numerical results show the effectiveness of the infill strengthening in terms of improvement of the infills OOP performance and thus of the overall structural response.